Response of the charophyte Nitellopsis obtusa to heavy metals at the cellular, cell membrane, and enzyme levels

Abstract

The responses of the freshwater macroalga Nitellopsis obtusa to heavy metal (HM) salts of Hg, Cd, Co, Cu, Cr, and Ni were assessed at different levels: whole-cell mortality (96-h LC(50)), in vivo cell membrane (45-min depolarization of resting potential, EC(50)), and enzyme in plasma membrane preparations (K+, Mg2+-specific H+-ATPase inhibition, IC(50)). To measure ATPase activity, a novel procedure for isolation of plasma membrane-enriched vesicles from charophyte cells was developed. The short-term ATPase inhibition assay (IC(50) from 6.0 x 10(-7) to 4.6 x 10(-4) M) was slightly more sensitive than the cell mortality test (LC(50) from 1.1 x 10(-6) to 2.6 x 10(-3) M), and the electrophysiological test with the end point of 45-min depolarization of resting potential was characterized by less sensitivity for HMs (EC(50) from 1.1 x 10(-4) to 2.2 x 10(-2) M). The variability of IC(50) values assessed for HMs in the ATPase assays was close to that of LC(50) values in the mortality tests (CVs from 33.5 to 83.5 and from 12.4% to 57.7%, respectively), whereas the EC(50) values in the electrophysiological tests were characterized by CVs generally below 30%. All three end points identified two separate HM groups according to their toxicity to N. obtusa: Co, Ni, and Cr comprised a group of less toxic metals, whereas Hg, Cu, and Cd comprised a group of more toxic metals. However, the adverse effects within each group were discriminated differently. For example, the maximum difference between the highest and lowest LC(50) for the group of less toxic metals in the long-term mortality test was approximately 60% of the response range, whereas the corresponding difference in IC(50) values in the ATPase assay was 30%. In contrast, the LC(50) values of the more toxic metals occupied only 10% of the response range, whereas the IC(50) values were spread over 70%. Further investigation should be done of the underlying mechanism or mechanisms responsible for the observed differences in the dynamic range of a particular end point of the groups of toxicants of varying strength.

Gene expression patterns in Euglena gracilis: Insights into the cellular response to environmental stress

“…While, the decreased expression of the H + -ATPase mRNA may be explained as a response to Cr-induced membrane depolarization (Manusadzianas et al, 2002), the decreased mRNA level for E. gracilis GAPDH genes, one 75% similar to Plantae-algae GAPDH (chloroplast located) (DN976408) and the other 60% identical to the Kinetoplastidae GAPDH (glycosome located) (DN976404) is presumably a consequence of alterations of the glycolytic function induced by the metal (Henze et al, 1995).…”

Phycoremediation of Chromium (VI) by Nitella and impact of calcium encrustation

“…This was checked by means of picking the cells with a spatula. A cell was judged to be dead when picked up if there was a loss in the turgor pressure, a condition in which a cell bends on the spatula and loses its cylindrical shape [18].…”

Nickel in the Environment and Its Role in the Metabolism of Plants and Cyanobacteria

“…Furthermore, toxicity thresholds for nickel depend, as for any other toxic metal, on the growth conditions including irradiance, pH, and speciation of the metal. For the charophyte Nitellopsis, for example, a 4-day LC 50 of 290 µM was found [97]. For the submerged water macrophytic plant Elodea, a 7-day lethal concentration of 200 µM was reported [98], and for the fl oating macrophytic plant Spirodela a 14-day EC 50 of around 80 µM was observed [99].…”

“…When considering the impacts of nickel pollution on plants one should keep in mind that nickel is much less toxic to plants than other important environmental contaminants, in particular copper. For submerged waterplants, for example, nickel is more than hundred times less toxic than copper [97,98]. This is particularly important since nickel pollution in most cases occurs together with copper pollution, as described in more detail below.…”